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Hubs for Dallas 1-Wire (also known as MicroLan) networks.
First the bad news: I do not know of a commercial source for a hub. I believe that most hubs will be based on the DS2407 switch. If you don't mind making your own hardware, you'll find information about a well tested hub design at Simon's Page.
The people in the Dalsemi Weatherlist discussion group got together and did a joint order for pcbs and parts for a hub in the first half of 2002. Maybe one of theirs will come on the market, maybe someone can tell me of a commercially available hub. I did a guide to assembling that kit which you may find useful if you have one. Sadly, the discussion group is no more. Click here for information on it and alternatives.
In any case, what is a hub? What is it good for?
The purpose of a hub is to split up a big network into smaller segments.
One wire goes from the computer to the hub. From the hub, two sub-nets emerge. Software in the computer turns on one or the other of the sub-nets at any given time. The wires to the sub-nets can themselves go into a hub. The secondary hub can give rise to a "sub-sub-net". In principle, this can be repeated as often as you like.
Having a net split up into sub-nets can increase reliability. If a given sub-net is playing up, you just never "switch it on". If you have two devices that for some reason clash, you just put them on different sub-nets so that they are not both on "the" net at the same time.
All a fine theory, and if that's what it takes, I suppose that's what I'll have to do. Most of the reading I've done suggests that the 1-Wire net is supposed to manage with many, many devices on a single wire without all of the overhead of splitting the net up into sub-nets. Ah well.
A 1-Wire net is most likely to behave well if it is one long wire with sensors and actuators connected nearly directly to it. If you have a situation where you need to have the net branch into multiple "arms", you are more likely to have reliability problems... problems which a hub should solve.
Click here for a long essay in pdf format. It discusses 1-Wire hubs in general, and then goes on to discuss how to program them, using Delphi. Click here for the Delphi sourcecode in a zip file.
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